Glazing assembly comprising a substrate provided with a stack of thin layers for solar protection and / or thermal insulation

ABSTRACT

A glazing assembly is provided made of at least one transparent substrate having a stack thereon that includes an alternation of n functional layers and n−1 coatings, wherein the functional layers have reflection properties in the infrared and/or solar radiation and where n≧1 and where, in order to maintain the quality of the stack when the substrate is subjected to a heat treatment step, at least one of the following must be satisfied:  
     the coating placed on top of at least one of the functional layers includes at least one barrier layer providing a barrier to at least oxygen and water; and  
     at least one absorbent or stabilizing layer made of a material capable of absorbing or stabilizing the consituent material of the functional layer forms a part of either the coating placed on top of the functional layer and under the barrier layer or the coating placed beneath the functional layer; and a method for production of the glazing assembly.

[0001] The invention relates to transparent substrates, in particularmade of a rigid inorganic material such as glass, the said substratesbeing coated with a stack of thin layers comprising at least one layerhaving a metallic-type behaviour able to act on solar radiation and/orlong-wavelength infrared radiation.

[0002] The invention relates more particularly to the use of suchsubstrates to manufacture thermal-insulation and/or solar-protectionglazing assemblies. These glazing assemblies are intended to equip bothbuildings and vehicles, with a view in particular to decreasing theair-conditioning load and/or to reducing excessive overheating caused bythe ever growing extent of glazed surfaces in passenger compartments.

[0003] A known type of multilayer stack for giving the substrates suchproperties consists of at least one metallic layer, such as a silverlayer, which is placed between two coatings of dielectric material ofthe metal-oxide type. This stack is generally obtained by a successionof depositions carried out using a vacuum technique, such as sputtering,optionally assisted by a magnetic field. Two very thin metal layers mayalso be provided on either side of the silver layer, the subjacent layeracting as a tie layer for nucleation and the overlayer as a protectiveor “sacrificial” layer so as to prevent degradation of the silver if theoxide layer which is on top of it is deposited by sputtering in thepresence of oxygen.

[0004] Stacks of this type, having one or two base layers of silver, arethus known from European Patents EP-0,611,213, EP-0,678,484 andEP-0,638,528.

[0005] Currently, there is an increasing demand for these low-emissivityor solar-protection glazing assemblies which have in additioncharacteristics inherent in the substrates themselves, in particularaesthetic characteristics (so that they can be shaped), mechanicalproperties (so that they are stronger) or safety characteristics (sothat they do not cause injury in the event of breakage). This requiresthe glass substrates to be subjected to heat treatments known per se, ofthe bending, annealing and toughening type. Laminated-type glazingassemblies intended to be fitted into vehicles, which are nowadaysalmost all curved and/or toughened, are particularly intended.

[0006] It is therefore necessary to adapt the multilayer stack in orderto preserve the integrity of the functional layers of the silver-layertype, in particular to prevent their degradation. A first solutionconsists in significantly increasing the thickness of the thin metallayers, mentioned above, which surround the functional layers: in thisway it is ensured that any oxygen likely to diffuse from the ambientatmosphere and/or migrate from the glass substrate at high temperaturebe “captured” by these metal layers, by oxidizing them, without itreaching the functional layer(s).

[0007] This solution is not without drawbacks: since the two metallayers readily oxidize “instead of” the silver layers, they lead inparticular to a great increase in the light transmission T_(L); it isthus possible to obtain a low-emissivity or solar-protection glazingassembly, which is curved or toughened, having a value of T_(L) greaterthan 75 and up to 80%, though this value was much lower before the heattreatment. In particular, reference may be made to Patent ApplicationEP-A-0,506,507 for the description of such a “toughenable” stack with asilver layer placed between a tin layer and a nickel-chrome layer.However, it is clear that the coated substrate before heat treatment wasregarded only as a “semi-finished” product and the optical propertiesfrequently made it unusable as such. It was therefore necessary todevelop and manufacture, in parallel, two types of multilayer stack, onefor the non-curved/non-toughened glazing assemblies and the other forglazing assemblies intended to be toughened or curved, which maycomplicate matters, in particular in terms of stock and productioncontrol.

[0008] An improvement proposed in Patent EP-0,716,250 has made itpossible to overcome this constraint: the teaching of this documentconsists in designing a stack of thin layers such that its optical andthermal properties remained virtually unchanged, whether or not thesubstrate, once coated with the stack, underwent a heat treatment. Sucha result is achieved by combining two characteristics;

[0009] on the one hand, provided on top of the functional layer(s) is alayer made of a material capable of forming a barrier to oxygendiffusion at high temperature, which material itself does not undergochemical or structural modification at high temperature which wouldresult in modification in its optical properties. This material may thusbe silicon nitride Si₃N₄ or aluminium nitride AlN;

[0010] on the other hand, the functional layer(s) is (are) directly incontact with the subjacent dielectric coating, in particular zinc oxideZnO.

[0011] Although this solution allows the substrate effectively tomaintain a T_(L) level and an appearance in external reflection which,after heat treatment, are quite constant, it is still capable ofimprovement, in that it has been observed with this type of stack thatoptical defects, sometimes visible to the naked eye, could appear afterheat treatment, these very often being in the form of a speckling ofbright spots of the “pinhole” type or having a slightly fuzzyappearance, which is obviously prejudicial in terms of the aestheticappearance and of productivity since this may lead to an abnormally highscrap rate, most particularly if these glazing assemblies arecurved/toughened glazing assemblies, which may or may not be of thelaminated types intended for fitting into vehicles of the motor-vehicletype, in which very strict standards impose a very high optical quality.

[0012] The object of the invention is therefore to succeed in remedyingthis drawback, in particular by developing a novel type of stack havinga functional layer or layers, of the type of those described previously,which stack is able to undergo high-temperature heat treatments of thebending/toughening or annealing type, while preserving its opticalquality.

[0013] The subject of the invention is a glazing assembly comprising atleast one transparent substrate provided with a stack of thin layerswhich includes an alternation of n functional layer(s) having reflectionproperties in the infrared and/or in solar radiation, in particular ofan essentially metallic nature, and of (n+1) “coatings”, with n≧1. Thesaid “coatings” are composed of a layer or a plurality of layers, atleast one of which is made of a dielectric material. These functionallayers and these coatings are arranged so that the (each) functionallayer is placed between two coatings.

[0014] With a view to preserving the optical quality of the stack in thecase where the substrate once provided with the stack is subjected to aheat treatment of the toughening, bending, annealing type:

[0015] on the one hand, the coating placed on top of the functionallayer, or on top of one of the functional layers, and in the latter casepreferably the nth layer, includes at least one “barrier” layer made ofa material capable of forming a barrier at least to oxygen and water;and

[0016] on the other hand, at least one “absorbent” or “stabilizing”layer made of a material capable of “absorbing” or “stabilizing” theconstituent material of the said functional layer forms part of:

[0017] either the coating placed on top of the said functional layer andunder the “barrier” layer;

[0018] or the coating placed under the said functional layer.

[0019] Preferably, the barrier layer is made of a material capable ofalso forming a barrier to the constituent material of the functionallayer.

[0020] The inventors have in fact demonstrated that the appearance ofoptical defects after heat treatment of this type of stack of thinlayers arose essentially from the migration of part, even a very smallpart, of the constituent material of the functional layer into thelayers which are adjacent to it. The term “constituent material” isunderstood to mean, when the layer is metallic, both the metal elementin question and the possibly totally or partially ionized metal. Thus,when the functional layer is wade of silver, the migration of silverboth in the form of Ag and Ag⁺ into the upper layers, i.e. those placedon top of it, was observed, this migration resulting in the formation ofsilver “clusters” on the surface of the stack, creating an unattractivespeckling.

[0021] Two reasons for this migration have been proposed—on the onehand, a mechanical reason and, on the other hand, a chemical reason.

[0022] From the mechanical standpoint, when the stack is heated to hightemperature, in particular within the temperature range of from 550 to650° C. which is necessary for the usual operations of bending and/ortoughening the glazing assemblies, all the materials making up the thinlayers “react differently” to this thermal stress. The functional layermade of metal of the silver type will expand greatly and, in general,more than the other layers of the stack, in particular those based on adielectric which are contiguous with it. The functional layer willtherefore be in a high state of compression at high temperature, and thesilver, in metallic and/or ionic form, then tends to embrittle, with adecrease in the adhesion of the layer to the contiguous layers, until ithas a tendency to migrate into the other layers in order to relieve thethermomechanical stress to which it is subjected.

[0023] From the chemical standpoint, if this time the adjacent layers,and more particularly the layers placed on top of it, are not capable ofcompletely blocking this migration, the optical defects mentioned abovethen appear. This may be the case when there are, as dielectric coatingsplaced on top of the functional layer, known materials of themetal-oxide type, or even materials chosen for forming an oxygen barrierso as to prevent the migration of oxygen from the outside into thefunctional layer, as is the case with Si₃N₄.

[0024] The invention therefore consisted in providing a doubleprotection for the functional layer of the silver type.

[0025] It was important to continue to provide on top of the functionallayer at least one layer made of a material capable of preventing themigration of oxygen and water from the ambient atmosphere into thefunctional layer, this diffusion rising from the atmosphere proving tobe of greater magnitude and markedly more prejudicial to the integrityof the functional layer than the possible migration of oxygen whichstemmed this time from the glass. (However, provision may also be made,for maximum safety, also to place this type of “barrier” layer under thefunctional layer). This thus avoids any chemical modification of thefunctional layer, in particular by oxidation/hydration, which woulddecrease its thermal performance characteristics and would call intoquestion its optical quality, this chemical degradation phenomenon beinguncontrollable.

[0026] However, the invention adds to this first protection, accordingto a first variant, a means for capturing, and absorbing the silverwhich would tend to migrate out of the layer, this being achieved withthe aid of a layer capable of receiving a certain amount of constituentmaterial of the functional layer which is “in excess” under thethermomechanical stress. This so-called “absorbent” layer thus makes itpossible to stop the migration into the other layers of the stack as faras the external atmosphere.

[0027] Its place in the stack can be varied. If it is placed on top ofthe functional layer, it is preferable, in order for it to be able tofulfil its role, for it to be under the barrier layer mentionedpreviously in order to prevent there being any migration through thebarrier layer, creating the optical defects mentioned previously, i.e.the formation of “clusters” of material coming from the functionallayer, in particular silver, which are responsible for the unattractivespeckling. However, provision may also be made for it to be placed underthe functional layer.

[0028] In fact, the “absorbent” layer is to be chosen so that itpreferably has at least two properties: it is important, on the onehand, that the material of which it is composed has a good chemicalaffinity with the material of the functional layer and, on the otherhand, that the material of the absorbent layer is able to capture the“excess” material of the functional layer, it being possible for themethod of incorporating this “excess” material to be carried out invarious ways, in particular by incorporation of the interstitial type orof the vacancy type.

[0029] According to a second variant, it is preferred to use not an“absorbent” layer but rather a “stabilizing” layer. In the sense of theinvention, “stabilizing” means that the nature of the layer in questionis selected so as to stabilize the interface between the functionallayer and this layer. This stabilization leads to an increase in theadhesion of the functional layer to the layers which surround it, andthus resists the migration of its constituent material generally in adirection taking it away from the carrier substrate.

[0030] It has turned out that one particularly advantageous material forforming this “stabilizing” layer is zinc oxide, preferably placed on topof the functional layer in order to resist in an optimum manner thediffusion from the opposite side of the stack from the class substrate,either directly or via a thin metal layer of the sacrificial type (thethickness is generally about 0.5 to 2 nm). (It may also be under thefunctional layer, preferably directly in contact with it). ThisZnO-based “stabilizing” layer advantageously has a thickness of at least5 nm, in particular between 5 and 25 nm.

[0031] The invention applies not only to stacks having only a single“functional” layer placed between two coatings. It also applies tostacks which include a plurality of functional layers, in particular twofunctional layers alternating with three coatings, of the typedescribed, for example, in Patent EP-0,638,528, or three functionallayers alternating with four coatings, of the type described, forexample, in Patent EP-0,645,352.

[0032] If the stack thus uses several functional layers, it has provedto be the case that it was often advantageous for the last functionallayer, the one furthest away from the carrier substrate, of the stack tobe provided both with a barrier layer and with an absorbent orstabilizing layer, as it seems that it was the latter which was most“exposed” because of its position in the stack, in the sense that it wasthe most likely to be oxidized by the ambient atmosphere and the onefrom which part of its constituent material could migrate the mosteasily as far as the external surface of the last layer of the stack.

[0033] Of course, provision may be made for all the functional layers tobe thus provided with a barrier layer and with an absorbent orstabilizing layer according to the invention, in particular made ofsilver or a metal alloy containing silver.

[0034] The barrier layer according to the invention is preferably chosenfrom dielectric materials whose refractive index is advantageouslysimilar to those normally used in this type of sack, i.e. lying inparticular between 1.7 and 2.5. It may thus “optically” replace thedielectric layers of the metal-oxide type and combine an interferentialoptical function with a barrier function.

[0035] The barrier layer is, in particular, based on silicon compoundsof the silicon oxide SiO₂, silicon oxycarbide SiO_(x)C_(y) or siliconoxynitride SiO_(x)N_(y) type. It may also be based on nitrides, of thesilicon nitride Si₃N₄ or aluminum nitride AlN type, or a mixture of atleast two of these compounds.

[0036] It may also be chosen to be of the carbide type, such as SiC,TiC, LiC and TaC, but then it is preferred to limit it to thicknesseswhich are not too great, because of their absorbent character which maypenalize the stack in terms of the level of light transmission T_(L) ifit is desired to obtain a glazing assembly with a high T_(L).

[0037] In general, the geometrical thickness of the barrier layer isotherwise preferably selected, so that it is at least 10 nm, inparticular at least 15 nm or especially between 15 and 60 nm or moreespecially between 20 and 50 nm.

[0038] Let us now turn our attention to the arrangement in the stack andto the nature of the absorbent layer according to the first variant ofthe invention. It has been seen that it must enable the state ofcompression of the functional layer at high temperature to be reduced byallowing part of its material, particular in metallic or ionic form, tobe incorporated. It may be placed either directly in contact with thefunctional layer, under it or on top of it, or it is separated from itby at least one “interlayer” which is “permeable” to the migration ofthe material in metallic or ionic form at high temperature, without thisresulting in a chemical or structural modification of the saidinterlayer having a prejudicial impact on the optical appearance of thestack in its entirety. This interlayer or these interlayers, able to bebetween the functional layer and the absorbent layer are in particularthe thin metal layers which serve as nucleation layers or as sacrificiallayers with respect to the functional layer.

[0039] According to a first embodiment, the material of the absorbentlayer is chosen from a porous material, in particular a layer having aporosity of at least 2% and preferably between 5 and 25%. Porosity isdefined here by the relationship p %=1−(d₁/d₀), where d₀ is thetheoretical density of the material in question as a percentage and d₁its actual density. This porosity is often manifested, when the materialis a dielectric, by a reduction in its refractive index compared to itstheoretical index, approximately in the same proportions as its density.In order to provide a sufficient absorption capacity, provision isgenerally made for this porous layer to have a geometrical thickness ofat least 2 nm, in particular between 2 and 30 nm; it is possible to varyboth the porosity and the thickness in order to obtain the desiredeffect of complete absorption of the material of the functional layerwhich is “in excess”.

[0040] According to a first case, this porous layer may be essentiallymetallic, in particular made of a material chosen from at least one ofthe following metals: Ni, Cr, Nb, Sn, Ti, an alloy of the NiCr type orsteel. In this case, it is preferable to limit its thickness to a rangeof from 2 to 5 nm, as its optically absorbent nature would, if a thickerlayer were to be chosen, decrease the level of light transmission toosignificantly when it is desired to have a highly transparent glazingassembly.

[0041] According to a second case, the porous layer is chosen from adielectric material, in particular a material chosen from at least oneof the following oxides: zinc oxide ZnO, titanium oxide TiO₂, siliconoxide SiO₂ and aluminium oxide Al₂O₃. In this case, the layer may beappreciably thicker and also fulfil its interferential role in thestack.

[0042] The porosity of these various materials may be varied byadjusting the deposition conditions. Thus, when these layers aredeposited by sputtering, optionally assisted by a magnetic field, thechoice of the pressure within the deposition chamber makes it possibleto control the porosity of the layer; the higher the pressure of theinert gas, of the argon type, the greater the tendency for the porosityto increase.

[0043] According to a second embodiment, the material of the absorbentlayer consists of a material capable of reversibly or irreversiblyinserting the ions of the metal of the functional layer, and possiblythe un-ionized metal, and possibly ionizing the material at the momentof inserting it. This is in particular a material based on at least oneof the following components: tungsten oxide WO₃, nickel oxide NiO_(x),niobium oxide NbO_(x), iridium oxide IrO_(x), tin oxide SnO_(x), andvanadium oxide VO_(x), it being possible for these oxides to besubstoichiometric in terms of oxygen, and either hydrated or nonhydrated. In fact, these materials, in particular tungsten oxide, arewell-known for their properties of reversibly inserting cations of theAg⁺ type in electrochromic windows or devices.

[0044] The thickness of this type of insertion layer can be varied, inparticular depending on its intrinsic insertion capacity with respect toeach of the materials mentioned. Preferably a layer of at least 1 nm, inparticular between 1 and 50 nm, preferably between 2 and 30 nm, isprovided.

[0045] According to a third embodiment, the absorbent layer essentiallyconsists of a metal (or of a metal alloy) capable of forming a definedor non-defined solid solution with the metal of the functional layerwhen it is metallic. Mention may be made in particular of at least oneof the following metals or metalloids: Cu, Pd, Zn, Au, Cd, Al and Si.The term “solid solution is understood to mean here an association whichis not necessarily strictly speaking an alloy, but one in which themetal of the absorbent layer can “dissolve” a certain amount of themetal of the functional layer into its matrix, forming a compound whichmay be of undefined stoichiometry, i.e. a metal which can incorporate avariable amount of metal of the functional layer, an amount “starting”from 0% and able to increase progressively.

[0046] Provision may also be made for the materials of the second andthird embodiments to have a porosity such as that defined in the firstembodiment.

[0047] Advantageously, provision may be made for at least one of thefunctional layers to be surmounted by a thin “sacrificial” metalliclayer which is at least partially oxidized, in particular having athickness of from 0.5 to 4 nm: the latter makes it possible to preservethe functional layer from oxidation, during the deposition of the stack,when the next layer is based on an oxide deposited by reactivesputtering in the presence of oxygen. The “sacrificial” layer thusoxidizes in place of the metal of the functional layer.

[0048] Provision may therefore be made for the metallic-type absorbentlayer, in particular one which is porous and/or capable of forming asolid solution, to be placed directly on top of the functional layer andtherefore also to act as a “sacrificial” layer. In this case, it must besufficiently thick so that, after it has oxidized during the depositionof the upper layer, there remains a sufficient thickness of non-oxidizedmetal capable of fulfilling its role as an absorber.

[0049] Advantageously, the stack comprises two functional layers, witheach of which are associated a barrier layer and an absorbent orstabilizing layer.

[0050] In the stack, the barrier layer or at least one of the barrierlayers may constitute the essential aspect of the coating in the senseof the invention. It may also be combined with other layers ofdielectric material and may, in particular, be surmounted by at leastone other layer based on a metal oxide or oxides, such as zinc oxideZnO, tin oxide SnO₂, titanium oxide TiO₂, niobium oxide Nb₂O₅, tantalumoxide Ta₂O₅, aluminium oxide Al₂O₃ and tungsten oxide WO₃, or anymixture of at least two of these oxides. There are in particular twoways of carrying out the deposition of this oxide layer: either, in theusual way, directly in the form of oxide or, in particular when itconstitutes the final layer of the stack, in the metallic form, itsoxidation then being carried out after its deposition, most particularlyduring the heat treatment in air of the substrate. Its thickness ispreferably chosen to be between 0.5 and 20 nm, in particular between 1and 5 nm, but of course it remains optional. The reasons may be many, inparticular they may take into account the rate of deposition of theselayers, the cost of the raw materials (the targets if a sputteringdeposition technique is used) and the refractive indices. The judiciouschoice of the layer or layers surmounting the barrier layer may alsotake into account the optimization of the adhesion of the stack to thesheet of thermoplastic polymer of the polyvinyl butyral PVB type whenthe substrate coated with the stack is mounted with a laminated glazingassembly. (In this regard, the teaching of Patent EP-0,433,136 may thusbe indicated). This choice may also take into account thechemical-corrosion and/or mechanical problems that the stack may have toovercome, for example depending on the atmosphere with which it willcome into contact, either during the process for manufacturing theglazing assembly (for example, the atmosphere during the heat treatment)or while it is being stored or once it has been installed.

[0051] Moreover, provision may also be made for the functional layer, orat least one of the functional layers, to be placed on a coating, thefinal layer of which facilitates wetting of the functional layer. Thismay more particularly be a wetting layer based on zinc oxide ZnO,niobium oxide Nb₂O₅ or tantalum oxide Ta₂O₅, or a sequence of two layersof this type. For further details, reference may be made to PatentsEP-0,611,213 and EP-0,678,434. It is not excluded for these wettinglayers, by choosing them so as to be porous, also to be able to fulfilthe role of absorbent layers or, by selecting their thickness and theirconfiguration, that of stabilizing layers.

[0052] According to one embodiment of the invention, at least one of thefunctional layers is surmounted by a coating comprising the sequenceabsorbent or stabilizing layer/barrier layer of the SnO₂/Si₃N₄ orWO₃/Si₃N₄ or ZnO/Si₃N₄ type, it being possible for Si₃N₄ to be replaced,for example, by AlN or by a mixture of AlN and Si₃N₄.

[0053] The glazing assembly according to the invention may also be suchthat, in particular in the case of a stack having two silver-basedfunctional layers, at least one of these layers, in particular the finalone, is on top of a coating comprising the sequence ZnO/Si₃N₄/ZnO.

[0054] This glazing assembly may also be such that at least one of thefunctional layers, in particular the first one, is on top of a coatingcomprising the sequence SnO₂/ZnO or Si₃N₄/ZnO.

[0055] According to a second embodiment, there is this time a sequenceof the absorbent or stabilizing layer/functional layer/barrier layertype (possibly with “interlayers” on either side of the functionallayer) with, in particular, a layer of SnO₂ or WO₃ or ZnO under thefunctional layer and a layer of Si₃N₄ and/or AlN on top of thefunctional layer.

[0056] The glazing assembly according to the invention includes at leastthe substrate carrying the stack, possibly combined with at least oneother substrate. They may all be clear, or coloured, particularly atleast one of the substrates may be made of bulk-coloured glass. Thechoice of the type of coloration will depend on the level of lighttransmission and/or on the calorimetric appearance which are desired forthe glazing assembly once its manufacture has been completed. Thus, forglazing assemblies intended for fitting into vehicles, standards demandthat the windscreen have a light transmission T_(L) of approximately75%, such a level of transmission not being required for the sidewindows or the sun-roof, for example. The tinted glasses which may beadopted are, for example, those which, for a thickness of 4 mm, have aT_(L) of from 65% to 95%, an energy transmission T_(E) of from 40% to80% and a dominant wavelength in transmission of from 470 nm to 525 nmcombined with a transmission purity of from 0.4% to 6% using the D₆₅illuminant, which may be “manifested” in the (L, a⁺, b⁺) colorimetrysystem by values of a⁺ and b⁺ in transmission of, respectively, between−9 and 0 and between −8 and +2.

[0057] These may be the glasses sold under the name PARSOL bySaint-Gobain Vitrage, in particular those having a verdigris tint. Theymay also be glasses of the so-called “TSA” range which are also sold bySaint-Gobain Vitrage, and glasses whose composition and properties arein particular described in Patents EP-0,616,883, EP-0,644,164,EP-0,722,427 and WO-96/00394.

[0058] The glazing assembly according to the invention may have alaminated structure, combining in particular at least two rigidsubstrates of the glass type using at least one sheet of a thermoplasticpolymer, so as to have a structure of the glass/stack of thinlayers/sheet(s)/glass type. In particular, the polymer may be based onpolyvinyl butyral PVB, ethylene-vinyl acetate EVA, polyethyleneterephthalate PET or polyvinyl chloride PVC.

[0059] The glazing assembly may also have a so-called laminated-glazingstructure which combines a rigid substrate of the glass type with atleast one sheet of polymer of the polyurethane type having energyabsorpton properties optionally combined with another layer of polymershaving “self-healing” properties. For more details on this type ofglazing assembly, reference may be made in particular to PatentsEP-0,132,198, EP-0,131,523 and EP-0,389,354. The glazing assembly maythen have a structure of the glass/stack of thin layers/sheet(s) ofpolymer type.

[0060] The glazing assemblies according to the invention are capable ofundergoing a heat treatment without damaging the stack of thin layers.They are therefore optionally curved and/or toughened. If they arecurved, in particular for the purpose of forming windows for vehicles,the stack of thin layers is preferably on an at least partiallynon-planar face. In a laminated structure, it is preferably in contactwith the sheet of polymer.

[0061] The glazing assembly may also be curved and/or toughened when itconsists only of a single substrate, that provided with the stack. Thisis then referred to as a “monolithic” glazing assembly. The glazingassembly may also be a multiple-glazing unit, in particular adouble-glazing unit, at least the substrate carrying the stack beingcurved and/or toughened. It is preferable in a multiple-glazingconfiguration for the stack to be placed so that it is on the sidefacing the sandwiched gas-filled cavity.

[0062] The glazing assemblies of the invention are, in a general way,preferably designed so as to have a light transmission value of from 50to 85%, in particular from 60 to 80%, with values of reflection R_(L)which are less than 20%, in particular less than 13%, and negativevalues of a⁺ and b⁺ in external reflection: it is thus possible inparticular to “cover” the entire range of T_(L) encountered in windowsfor vehicles, with, in external coloration, a tint more towards theblue-greens, this currently being judged to be quite aesthetic.

[0063] The invention also relates to the process for manufacturing theglazing assemblies, which may consist in depositing the stack of thinlayers on its class substrate using a vacuum technique of the sputteringtype, optionally assisted by a magnetic field (without excluding thepossibility that the first layer or first layers is or are depositedusing another technique, for example using a thermal decompositiontechnique of pyrolysis type), and then in carrying out a heat treatmentof the bending/toughening or annealing type on the coated substratewithout impairing its optical quality.

[0064] The details and advantageous characteristics of the inventionwill emerge from the following non-limiting examples illustrated bymeans of FIG. 1.

[0065]FIG. 1 shows a stack according to the invention, but theproportions between the thicknesses of the various materials are notrespected so that it is easier to examine it.

[0066] In all the examples which follow, the stack is deposited on thesubstrate 1, which is a substrate made of clear silica-soda-lime glass 2mm in thickness. The stack is decomposed into two silver functionallayers 3, 6 with identical thicknesses or with different thicknesses,the first layer 3 having a smaller thickness than that of the secondlayer 6 in accordance with the teaching of Patent EP-0,638,528. A thinat least partially oxidized metallic “sacrificial” layer 4, 7 isdeposited on each of the functional layers 3, 6.

[0067] Under each of the functional layers 3, 6 is a layer or aplurality of superimposed layers based on a dielectric material, theselayers being referenced 2 a, 2 b and 5 a, 5 b.

[0068] On the final functional layer 6, counting from the substrate, andon top of the sacrificial layer 7, there is a layer or a superpositionof layers of dielectric material 8 a, 8 b.

[0069] There is therefore a structure using a first coating whichcombines the layers 2 a and 2 b and a silver layer 3, a second coatingwhich combines the layers 4, 5 a and 5 b and a second silver layer 6,and a third coating which combines the layers 7, 8 a and 8 b.

[0070] According to a first series of examples, Examples 1 to 3:

[0071] the sacrificial layers 4, 7 are made of Nb

[0072] the layers 2 a are made of SnO₂

[0073] the layers 5 a are made of Si₃N₄

[0074] the layers 5 b are made of ZnO

[0075] the layers 8 b are made of Si₃N₄ and

[0076] the layers 3, 6 are made of silver.

[0077] In the various examples, only the nature of layer 8 a chances. Inthe sense of the invention, the Si₃N₄ layers 5 a and 8 b fulfil the roleof oxygen-barrier layers with respect to the silver layers 3 and 6,respectively, the “absorbent” layer in the sense of the invention beingthe layer 8 a, which is therefore capable of absorbing a certain amountof silver migrating from the silver layer 6 on top of (or beneath) whichit is deposited.

[0078] In all these examples, the layers of the stack are successivelydeposited by sputtering assisted by a magnetic field, but any otherdeposition technique may be envisaged as long as it allows good controlof the thicknesses of the layers to be deposited.

[0079] The deposition apparatus comprises at least one sputteringchamber provided with cathodes fitted with targets made of theappropriate materials under which the substrate 1 passes in succession.These deposition conditions for each of the layers are as follows:

[0080] the silver-based layers 3, 6 are deposited using a silver target,at a pressure of 0.8 Pa in an argon atmosphere,

[0081] the SnO₂-based layers 2 a are deposited by reactive sputteringusing a tin target, at a pressure of 0.8 Pa and in an argon/oxygenatmosphere having 36% of oxygen by volume,

[0082] the Nb-based layers 4, 7 are deposited using a niobium target,again at the same pressure and in an argon atmosphere,

[0083] the Si₃N₄ layers 5 a, 8 b are deposited by reactive sputteringusing a silicon target doped with boron or with aluminium, at a pressureof 0.8 Pa in an argon/nitrogen atmosphere having 20% of nitrogen byvolume, and

[0084] the ZnO layers 2 b and 8 b are deposited by reactive sputteringusing a zinc target, at the same pressure and in an argon/oxygenatmosphere having 40% of oxygen by volume.

[0085] The power densities and the run speeds of the substrate 1 areadjusted in a known manner in order to obtain the desired layerthicknesses.

EXAMPLE 1

[0086] In this example, the layer 8 a is made of tungsten oxide WO₃obtained by the reactive sputtering of a W target at a pressure of 0.8Pa in an argon/oxygen atmosphere having 20% of oxygen by volume.

EXAMPLE 2

[0087] In this example, the layer 8 a is made of “porous” zinc oxidedeposited at a pressure of 1.2 Pa, significantly greater than thatenvisaged for the layers 2 b and 5 b. Its measured porosity is 15%.

EXAMPLE 3

[0088] In this example, the layer 8 a is made of SnO₂ deposited like thelayer 2 a.

[0089] Table 1 below specifies, for each of the three examples, thenature and the thicknesses (in nanometers) of the layers of the stack inquestion. TABLE 1 EXAMPLE 1 EXAMPLE 2 EXAMPLE 3 Glass (1) — — — SnO₂(2a) 20 20 20 ZnO (2b) 17 17 17 Ag (3) 9 9 9 Nb (4) 0.7 0.7 0.7 Si₃N₄(5a) 65 65 65 ZnO (5b) 25 25 25 Ag (6) 9 9 9 Nb (7) 0.7 0.7 0.7 Layer 8a(8a) (WO₃): 2 (ZnO): 2 (SnO₂): 2 Si₃N₄ (8b) 37.5 37.5 37.5

[0090] Next, each of these coated substrates was subjected to a heattreatment above 620° C., then curved and joined to a substrate of thesame kind, but uncoated, and having the same curvature by means of athermoplastic sheet of polyvinyl butyral 0.80 mm in thickness by hotcalendering in a known manner so as to have a laminated substrate(1)/multilayer/PVB/substrate (2) structure, with the face of thesubstrate 1 on which is placed the multilayer stack which is non-planar,in a fitting of the motor-vehicle windscreen type.

[0091] Table 2 below indicates, for each of these examples:

[0092] A. the light transmission T_(L) in % (D₆₅ illuminant),

[0093] the energy transmission T_(E) in %,

[0094] the values of a⁺ and b⁺ in the (L, a⁺, b⁺) colorimetry system intransmission, a⁺ (T) and b⁺ (T),

[0095] the external light reflection R_(L) in % (D₆₅ illuminant), and

[0096] the values of a⁺ and b⁺ in the (L, a⁺, b⁺) colorimetry system inreflection, a⁺ (R) and b⁺ (R), on the one hand, for the coatedsubstrates (1) before bending and laminating (“monolithic”) and, on theother hand, for the coated substrates (1) once they have been curved andassembled into a laminated glazing assembly (“laminated”). TABLE 2 T_(L)T_(E) a* (T) b* (T) R_(L) a* (R) b* (R) Example 1 monolithic 80 51 −2.11.9 5 −1 −1.5 laminated 75 42 −2.9 5.9 11 −1.7 −16.6 Example 2monolithic 90 51 −2.1 1.9 5.5 −1.1 −1.5 laminated 75 41 −3 5.7 10.5 −2−14.7 Example 3 monolithic 80 51 −2.1 1.9 5.5 −1 −1.5 laminated 75 41 −35.7 11 −2.2 −14.5

[0097] Furthermore, the optical quality of the coated substrates oncethey have been curved is equivalent to the quality they had before heattreatment—there was no visible appearance of speckling or the appearanceof any residual fuzziness.

[0098] The following conclusions may be drawn from these results:

[0099] even for very small thicknesses, the absorbent layers 8 a, eitherof the “porous” type (ZnO) or of the Ag⁺-insertion type (WO₃, SnO₂), aresufficiently effective for relaxing the stresses in the final silverlayer 6, by absorbing the “excess” silver therein, and thus foreliminating the random optical degradation problems which could appearin similar stacks, but which do not have this type of layer;

[0100] the stack is not adversely affected, thermally or optically, bythe “additional” absorbent layers: the glazing assemblies remain withinthe blue-greens in reflection (a⁺ (R) and b⁺ (R) are both negative),whether they are a “monolithic” or a “laminated” glazing assembly, andit is possible to maintain T_(L) values of at least 75% in the laminatedcase, this being of importance in the motor-vehicle field when this typeof glazing assembly is used as a windscreen,

[0101] since the benging is a heat treatment, which may be regarded asbeing mechanically and thermally even more “stressful” than thetoughening operation, it is therefore also possible, a fortiori, to usethese glazing assemblies as non-curved toughened glazing assemblies, forexample having a double-glazing structure used in buildings, and toobtain the same optical quality; and

[0102] it should also be noted that the advantage of the stacks whichare described in Patent EP-0,718,250 is maintained in the sense that thethermal operation of the glazing assembly not only preserves its opticalquality (this was the object of the present invention) but furthermore,in particular because of the presence of the Si₃N₄ barrier layers, doesnot significantly modify its optical/thermal properties (the decrease inT_(L) in the laminated assembly compared to the monolithic assemblyarising, of course, from the addition of the sheet of PVB and the secondglass).

[0103] An Example 4 was also produced, with certain modificationscompared to the previous examples, modifications consisting essentiallyin using titanium-based layers (4) and (7), in adding a ZnO layer,called below layer (5 a′), between the sacrificial layer (4) and theSi₃N₄-based layer (5 a) and finally in using as layer (8 a) a“stabilizing” layer made of non-porous (or hardly porous) ZnO.

[0104] Table 3 below collates the succession of layers with theirthicknesses in nm (the numbers in brackets also indicate the mostadvantageous range of thicknesses for each of the layers): TABLE 3EXAMPLE 4 Glass (1) — SnO₂ (2a) 17 - (5-20) ZnO (2b) 17 - (5-20) Ag (3)9 - (8-12) Ti (4) 1 - (0.5-1.5) ZnO (5a′) 10 Si₃N₄ (5a) 55 ZnO (5b) 20Ag (6) 9 - (8-12) Ti (7) 1 - (0.5-1.5) ZnO (8a) 10 Si₃N₄ (8b) 25

[0105] Preferably, the sum of the geometrical thicknesses of the layers(5 a′+5 a+5 b) is between 70 and 90 nm and the sum of the geometricalthicknesses of the layers 8 a and 8 b is between 30 and 50 nm.

[0106] In this stack, there is again the Si₃N₄ barrier layer (8 b), anda non-porous (or hardly porous) ZnO “stabilizing” layer (8 a). The othernon-porous or hardly porous ZnO layer (5 a′) may contribute to thestabilizing effect obtained by the ZnO layer (8 a).

[0107] Table 4 below indicates the photometric values (already explainedin the case of Table 2) of the substrate thus coated and then laminatedunder the same conditions as previously, with, in addition, the energyreflection value R_(E) in percentages: TABLE 4 Ex. 4 (laminated) T_(L)80.5% T_(E) 47% a* (T) 2.6 b* (T) 2.6 R_(L) 9.5% a* (R) −2.0 b* (R) −7.8R_(E) 34.5

[0108] Another example, Example 4a, was produced by repeating the stackin Example 4 but by slightly modifying the chemical nature of the Si₃N₄final layer (8 a): in accordance with the teaching of Patent ApplicationFR97/09223 of Jul. 21, 1997, this final layer was “doped” in that itcontains a small quantity of a metal, in this case aluminium, in aproportion of approximately 10 at. %; this “doping” makes it possible toincrease the resistance of the Si₃N₄ layer to corrosive species likelyto be present in the atmosphere where the subsequent heat treatment ofthe substrate is carried out, in particular species of the Na₂O type.

[0109] Finally, an Example 5 was produced, similar to Example 4, butusing under the first silver layer (3) not an SnO₂/ZnO sequence but anSi₃N₄/ZnO sequence. Furthermore, it was chosen to affix to each of thesilver layers (3) and (6) not only Ti sacrificial layers (4) and (7) ontop of them but also thin layers, called (2 c) and (2 c′) below, alsomade of Ti, just below them. However, it should be noted thatadvantageous stacks are also produced without these Ti sacrificiallayers (4), (7) and/or without these Ti sublayers (2 c)—they aretherefore optional.

[0110] Table 5 is the succession of layers: TABLE 5 EXAMPLE 5 Glass (1)— SnO₂ (2a)  9 ZnO (2b) 21 Ti (2c)  1 Ag (3)  9 Ti (4)  1 ZnO (5a′) 16Si₃N₄ (5a) 57 ZnO (5b) 16 Ti (2c′)  1 Ag (6) 10 Ti (7)  1 ZnO (8a) 20Si₃N₄ (8b) 18

[0111] In this particular case there is again the Si₃N₄ barrier layer (8b) and, as in Example 4, a non-porous or hardly porous ZnO “stabilizing”layer (8 a), the effect of which may be improved by the presence of thesubjacent layer (5 b) of ZnO which is also non-porous or hardly porous.

[0112] Example 5a consisted in producing an example identical to Example5, but by “doping”, as in Example 4a, the Si₃N₄ final layer 8 a withaluminium.

[0113] The invention therefore makes it possible to combine two verysignificant advantages when these stacks are intended to undergo heattreatments, by an advantageous combination of two types of layersintended to “contain” the silver layers and to preserve the integrity oftheir constituent material.

[0114] This application is based on French Priority ApplicationFR96/15265, filed in the French Patent Office on Dec. 12, 1996, theentire contents of which are hereby incorporated by reference.

[0115] Obviously, additional modifications and variations of the presentinvention are possible in light of the above teachings. It is thereforeto be understood that within the scope of the appended claims, theinvention may be practiced otherwise than as specifically describedherein.

1. A glazing assembly comprising at least one transparent substrate anda stack of thin layers thereon, wherein said stack of thin layerscomprises n functional layers having reflection properties in theinfrared, in solar radiation or in both, and (n−1) coatings, whereinsaid coatings comprise one or more layers, at least one of which in madeof a dielectric material, said functional layers and said coatingsalternating so that each functional layer is placed between twocoatings, wherein n≧1; wherein, when the substrate is subjected to aheat treatment selected from the group consisting of toughening, bendingand annealing, in order to preserve the optical quality of the stack atleast one of the following must be satisfied: the coating placed on topof at least one of the functional layers includes at least one barrierlayer comprising a material forming a barrier to at least oxygen andwater; or at least one absorbent layer comprising a material capable ofabsorbing the constituent material of the said functional layer or alayer that is stabilizing with respect to the said constituent materialforms at least a part of: (a) either the coating placed on top of thefunctional layer or under the barrier layer; or (b) the coating placedunder the functional layer.
 2. The glazing assembly according to claim1, wherein at least one of said n functional layers comprises a metallayer.
 3. The glazing assembly according to claim 1, wherein the stackis a single functional layer placed between two coatings.
 4. The glazingassembly according to claim 1, wherein the stack has two functionallayers alternating with three coatings.
 5. The glazing assemblyaccording to claim 1, wherein at least one of the functional layers ismade of silver or of a metal alloy containing silver.
 6. The glazingassembly according to claim 1, wherein the barrier layer comprises amaterial selected from the group consisting of SiO2, SiOxCy, SiOxNy,Si₃N₄, AlN, and mixtures thereof.
 7. The glazing assembly according toclaim 6, wherein the barrier layer has a geometrical thickness greaterthan or equal to 10 nm.
 8. The glazing assembly according to claim 1,wherein the absorbent layer is made of a porous material.
 9. The glazingassembly according to claim 8, wherein the porous absorbent layer has ageometrical thickness of at least 2 nm.
 10. The glazing assemblyaccording to claim 8, wherein the porous absorbent layer consistsessentially of a metal selected from the group consisting of Ni, Cr, Nb,Sn, Ti, NiCr alloys and steel.
 11. The glazing assembly according toclaim 10, wherein said porous absorbent layer has a thickness of from 2to 5 nm.
 12. The glazing assembly according to claim 8, wherein saidporous absorbent layer is made of a dielectric material
 13. The glazingassembly according to claim 1, wherein the absorbent layer is aninsertion absorbent layer made of a material capable of reversibly orirreversibly inserting metal cations from the n functional layer(s). 14.The glazing assembly according to claim 13, wherein said metal cationsare Ag⁺ cations.
 15. The glazing assembly according to claim 13, whereinthe insertion absorbent layer has a thickness greater than or equal to 1nm.
 16. The glazing assembly according to claim 1, wherein the absorbentlayer consists essentially of a metal or a metal alloy capable offorming a defined or non-defined solid solution with a metal of thefunctional layer.
 17. The glazing assembly according to claim 1, whereinat least one of the functional layers is surmounted by a sacrificialmetallic layer which is at least partially oxidized and has a thicknessof from 0.5 to 4 nm.
 18. The glazing assembly according to claim 1,wherein the absorbent layer comprises a metal and forms part of thecoating placed on top of, and directly in contact with, the functionallayer and directly in contact with it, and the Aabsorbent layer alsoacts as a sacrificial layer.
 19. The glazing assembly according to claim1, wherein the stabilizing layer comprises zinc oxide, and has ageometrical thickness of at least 5 nm.
 20. The glazing assemblyaccording to claim 1, wherein the stabilizing layer forms part of thecoating placed on top of the functional layer, and is directly incontact with the functional layer or separated from the functional layerby a thin sacrificial layer.
 21. The glazing assembly according to claim1, wherein the stack comprises two functional layers, each of which isassociated with a barrier layer and an absorbent layer.
 22. The glazingassembly according to claim 1, wherein at least one of the barrierlayers is under the coating of at least one other layer made of Si₃N₄ ora metal oxide selected from the group consisting of ZnO, SnO₂, TiO₂,Nb₂O₅, Ta₂O₅, Al₂O₃, WO₃, and mixtures thereof.
 23. The glazing assemblyaccording to claim 1, wherein at least one of the functional layers isplaced on a coating, a final layer of which facilitates wetting of thefunctional layer, wherein the final layer is made of an oxide selectedfrom the group consisting of Ta₂O₅, Nb₂O₅ and ZnO.
 24. The glazingassembly according to claim 1, wherein at least one of the functionallayers is surmounted by a coating sequence of SnO₂/Si₃N₄, WO₃/Si₃N₄, orZnO/Si₃N₄.
 25. The glazing assembly according to claim 1, wherein atleast one of the functional layers is placed on top of a layer of WO₃,SnO₂ or ZnO and beneath a layer made of Si₃N₄, AlN or a mixture of Si₃N₄and AlN.
 26. The glazing assembly according to claim 1, wherein at leastone of the functional layers is on top of a coating sequence ofZnO/Si₃N₄/ZnO.
 27. The glazing assembly according to claim 1, wherein atleast one of the functional layers is on top of a coating sequencecomprising SnO₂/ZnO or Si₃N₄/ZnO.
 28. The glazing assembly according toclaim 1, wherein at least one of the transparent substrates is made ofclear or bulk-tinted glass.
 29. The glazing assembly according to claim1, wherein the assembly is laminated, combining at least two rigid glasssubstrates using at least one sheet of a thermoplastic polymer, with alaminate structure of glass substrate/stack of one or more thin layersof thermoplastic polymer/glass substrate.
 30. The glazing assemblyaccording to claim 1, wherein the assembly is an asymmetric laminatedglazing, combining a rigid glass substrate with at least one sheet ofpolyurethane-based polymer having energy absorption properties, with alaminate structure copmrising glass substrate/stack of one or more thinlayers of polyurethane based polymer.
 31. The glazing assembly accordingto claim 1, wherein the glazing assembly is curved.
 32. The glazingassembly according to claim 1, wherein the assembly is mounted as amonolithic assembly or as a multiple-glazing unit of the double-glazingtype, wherein at least the substrate carrying the stack is made oftoughened glass.
 33. The glazing assembly according to claim 1, whereinthe assembly has a T_(L) of from 50 to 85%, and an R_(L) of less than20%.
 34. The glazing assembly according to claim 33, wherein theassembly has negative values of a⁺ and b⁺ in external reflection.
 35. Aprocess for preparation of a glazing assembly in accordance with claim1, comprising: depositing one or more layers of the stack of layers onthe substrate by vacuum sputtering, optionally in the presence of amagnetic field and subjecting the resulting product to a heat treatmentselected from the group consisting of bending, toughening and annealingwithout impairing its optical quality.